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- A low‐latitude species pump: Peripheral isolation, parapatric speciation and mating‐system evolution converge in a marine radiationPublication . Almeida, Susana C.; Neiva, João; Sousa, Filipe; Martins, Neusa; Cox, Cymon; Melo‐Ferreira, José; Guiry, Michael D.; Serrao, Ester; Pearson, GarethGeologically recent radiations can shed light on speciation processes, but incomplete lineage sorting and introgressive gene flow render accurate evolutionary reconstruction and interpretation challenging. Independently evolving metapopulations of low dispersal taxa may provide an additional level of phylogeographic information, given sufficiently broad sampling and genome-wide sequencing. Evolution in the marine brown algal genus Fucus in the south-eastern North Atlantic was shaped by Quaternary climate-driven range shifts. Over this timescale, divergence and speciation occurred against a background of expansion-contraction cycles from multiple refugia, together with mating-system shifts from outcrossing (dioecy) to selfing hermaphroditism. We tested the hypothesis that peripheral isolation of range edge (dioecious) F. vesiculosus led to parapatric speciation and radiation of hermaphrodite lineages. Species tree methods using 876 single-copy nuclear genes and extensive geographic coverage produced conflicting topologies with respect to geographic clades of F. vesiculosus. All methods, however, revealed a new and early diverging hermaphrodite species, Fucus macroguiryi sp. nov. Both the multispecies coalescent and polymorphism-aware models (in contrast to concatenation) support sequential paraphyly in F. vesiculosus resulting from distinct evolutionary processes. Our results support (1) peripheral isolation of the southern F. vesiculosus clade prior to parapatric speciation and radiation of hermaphrodite lineages-a "low-latitude species pump". (2) Directional introgressive gene flow into F. vesiculosus around the present-day secondary contact zone (sympatric-allopatric boundary) between dioecious/hermaphrodite lineages as hermaphrodites expanded northwards, supported by concordance analysis and statistical tests of introgression. (3) Species boundaries in the extensive sympatric range are probably maintained by reproductive system (selfing in hermaphrodites) and reinforcement.
- Reproductive strategies and population genetic structure of Fucus spp. across a northeast Atlantic biogeographic transitionPublication . Almeida, Susana C.; Nicastro, Katy; Zardi, Gerardo I.; Pearson, Gareth; Valero, Myriam; A, SerrãoGeographical discontinuities in the composition of species assemblages are often mirrored by genetic clines and local adaptation in species that extend across such biogeographic disjunction. Species distributed across such biogeographic discontinuities are thus more prone to develop genetic clines and adaptations to environmental variation. The northwest coast of France encompasses a biogeographic boundary between cold- and warm-temperate marine ecosystems. Distinct hydrographic features characterize northern and southern shores, promoting physical oceanographic breaks that can affect dispersal and connectivity between populations. Furthermore, mosaics of contrasting conditions may affect local patterns of species assemblages and potential adaptive pressures. Along this stretch of coast, the intertidal habitat is largely dominated by brown algae of the genus Fucus, key structuring species common along North Atlantic shorelines. Fucus spiralis, F. guiryi and F. vesiculosus are sister species with different mating systems. They have extensive sympatric geographical distributions and distinct but overlapping vertical distributions in the intertidal zone. We examined genetic structure and diversity across this major environmental transition zone using neutral microsatellite markers to investigate patterns of differentiation between populations of each species inhabiting the two different biogeographic regions. We found contrasting results between the dioecious species (F. vesiculosus) and the two selfing hermaphroditic lineages (F. spiralis and F. guiryi). Genetic differentiation of northern and southern populations of F. vesiculosus followed the expectation from a hypothetical oceanographic discontinuity across this biogeographical transition zone, but this was not the case for the two hermaphroditic species. The former had higher genetic diversity and structure along the distribution range investigated whereas selfing hermaphrodites had less variability and were not geographically structured. Our results suggest that genetic patterns are correlated with this biogeographical transition zone but this effect is dependent on mating system, a determining factor affecting population structure. Additionally, other factors such as intertidal elevation may also play a role in observed difference in genetic structuring.